Photovoltaic module

ABSTRACT

A photovoltaic panel is supported, sealed and isolated from the environment by being encased in a reaction injection molded elastomer which encapsulates the back, sides and a portion of the front side of the photovoltaic panel.

FIELD OF THE INVENTION

The invention relates to photovoltaic cells for converting light intoelectrical energy and more particularly to an elastomer-encasedphotovoltaic panel which offers significant advantages in manufacturingand weather resistance.

BACKGROUND AND SUMMARY OF THE INVENTION

It has long been desirable to capture radiation, particularly visiblelight, to convert it directly into electrical energy through theutilization of photovoltaic cells. Many types of photovoltaic cells,often referred to as solar cells, have been considered and constructed.For example, single-crystal cells have been produced, as well as thoseproduced from gallium arsenide and other similar materials. In addition,thin film cells have been fabricated from microcrystalline, amorphous,compound or semiconductor material other than single crystalsemiconductor material, deposited in situ upon a substrate by chemicalvapor deposition, sputtering or other similar means. In use, these cellsare assembled in photovoltaic panels and modules which must withstandthe rigors of the environment and handling in commerce.

As used herein, the term photovoltaic panel or panel refers to acombination of a sheet of transparent material or other lamina, an arrayor group of photovoltaic cells interconnected to provide an output ofelectrical energy, and any backing sheet or material, which forms adevice capable of transforming incident radiation to electrical current.Such panels are traditionally comprised of a transparent front orradiation-facing sheet such as a glass or transparent polymer, laminatedwith layers of transparent conductors, photovoltaic materials,cell-connecting circuits, metals and other lamina which togethercomprise an operative photovoltaic panel. Thus, photovoltaic panels havetraditionally included a sheet of glass or other rigid transparentmaterial to protect the photovoltaic cell, and a back sheet of steel oraluminum metal or foil, with the various lamina being bonded together bya dielectric layer of plasticized polyvinyl butyryl or ethylenevinylacetate. In instances where a totally transparent photovoltaicpanel is desired, such as in a solar cell which serves as an automobilesun roof, a front and back sheet both of rigid transparent material isemployed.

After the initial assembly of the laminates which comprise thephotovoltaic panel, the edges of the panel have traditionally beensmoothed to provide a flush edge surface, and sealed with anon-conductive varnish followed by one or more layers of polyesterand/or polyurethane tape. After this sealing of the edges, the panel isenclosed in a peripheral frame of aluminum, steel, molded polymer orother rigid frame material. This method of sealing and framing theperiphery of the panel has been necessary to isolate the solar cell fromthe environment, and to provide a frame for the strengthening of thepanel and to provide a border to permit ease of handling and theattachment of connector boxes and the like for attachment of thephotovoltaic cell to an external electrical circuit. For example, asolar panel with a hardened foil back layer sandwiched between polyvinylfluoride resin sheets, and framed in rigid peripheral framing is shownin U.S. Pat. No. 4,401,839. This combination of a photovoltaic panelwith the frame, sealing means, connection means and ancillary supportingstructures is referred to herein as a photovoltaic module.

While existing methods for the production and framing of photovoltaicpanels have provided significant improvements in solar cell technologyover the years, it has been a desideratum to simplify the lamination andmanufacture of such panels and provide for a stronger module and a moreperfect seal to protect the edges or back panel of photovoltaic panels.For example, the lamination steps have previously required aconsiderable expenditure of labor, and the metal backing sheetspreviously used to protect the back of the panel may allow electricalleakage which turns a photovoltaic cell into a capacitor.

According to the invention, a photovoltaic module is provided whichcomprises a panel having front and back sides and edges forming aperimeter and at least one photovoltaic cell capable of convertingradiation incident on the front of the panel to electrical energy, withthe panel being partially encapsulated in a unitary, reaction-injectedmolded elastomer which forms a seal against a portion of the front sideof the panel bordering the perimeter, and continues around the perimeterand seals against at least a portion of the back side. In oneembodiment, the module further comprises means for establishing externalelectrical connection to the photovoltaic cell, including an internalportion electrically connected to the cell and an external portionextending from the panel, and the unitary elastomer further encapsulatesat least the internal portion of such connecting means.

The elastomeric casing is formed on a predetermined portion of aphotovoltaic panel by placing the panel in a mold having interior wallswhich cooperate with the predetermined portion to define a cavityencompassing the perimeter and at least a portion of the front and backof the panel, introducing a flowable reaction injection molding materialinto the cavity and curing the material to form the casing. For example,the panel could be placed in a mold including two cooperating moldsections having surfaces defining a chamber for receiving the panel,with one of the mold sections having seal means positioned to beadjacent the periphery of the front side of the panel to support thepanel within the panel receiving chamber and seal the portion of thepanel located interiorly of the seal means against the influx of fluid.The facing surfaces of the mold sections located exteriorly of the sealmeans are provided with a casing shaping portion which cooperates withthe seal means and the predetermined portion of the panel to define acavity when the mold sections are in contacting relationship.

The mold also includes inlet means for introducing the flowable reactioninjection molding material into the cavity when the mold sections arecontacting to form a closed mold. The casing shaping portion of the moldmay also define a cavity portion which includes at least the internalportion of the connecting means of the panel so that a portion of theconnecting means is imbedded in the cured reaction injection moldingmaterial. Preferably, the reaction injection molding elastomerencapsulates the back and perimeter edges of the panel and forms a sealagainst a portion of the front side of the panel bordering theperimeter. If desired, a stiffening structure such as metal, fibrous orpolymeric sheets or girders may be included within the elastomer to addto the rigidity of the photovoltaic module.

In a preferred embodiment, the module comprises a first sheet having afirst radiation-incident side and having a photovoltaic cell formedthereon; a second backing sheet, preferably having a comparable modulusof thermal expansion, adjacent and spaced from a back side of the firstsheet; and a unitary, reaction injection molded elastomer disposedbetween the back side of the first sheet and the second, the elastomerpartially encapsulating the first sheet, forming a seal against aportion of the front side of the first sheet bordering the perimeter,continuing around the perimeter of the first sheet and sealing againstat least a portion of the second sheet. The term unitary elastomer, asused herein, refers to a one-piece elastomer, one that is formed by asingle injection of an elastomer-forming material as described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a photovoltaic module constructed inaccordance with the present invention;

FIG. 2 is a schematic vertical sectional view of a first embodimenttaken along line 2--2 of FIG. 1;

FIG. 3 is a schematic vertical sectional view of a second embodimenttaken along line 3--3 of FIG. 1; and

FIG. 4 is a vertical sectional view of mold sections which are employedto produce the photovoltaic module shown in FIG. 1.

FIG. 5 is an overhead view of the mold section 102;

FIG. 6 is a partial sectional view showing the means for formingjunction box or connecting cavity 72 of the module shown in FIG. 2;

FIG. 7 is a vertical sectional view of the module assembly produced bythe mold shown in FIG. 4 after demolding and prior to trimming of theflash and runner polymer sections; and

FIG. 8 is a fragmented, sectional perspective view of an alternativeembodiment of the invention.

DETAILED DESCRIPTION

A wide variety of photovoltaic panels may be encapsulated in anelastomer produced by reaction injection molding (RIM). Any such panelhaving a front transparent substrate bearing at least one photovoltaiccell may be advantageously encapsulated according to the invention. Inthe preferred embodiment, there is illustrated in FIGS. 1-3 aphotovoltaic module embodying the present invention, designatedgenerally 10. The module 10 comprises a laminated central panel 12,including an array of photovoltaic cells 14, surrounded by a border 16which is formed from a RIM elastomer. Turning now to FIG. 2, the module10 is seen to include a transparent sheet or substrate 18, formed fromvarious materials such as glass or transparent polymers, through whichincident light illustrated at 20 passes. The module 10 includes a thinfilm semiconductor material 22. The thin film material 22 may be, forexample, a PIN microcrystalline thin film silicon-hydrogen cell array, athin film amorphous silicon panel or an array of single crystalphotovoltaic cells. Methods for the production of photovoltaic panelsare known in the art and will not be discussed further herein, otherthan to incorporate by reference U.S. Pat. No. 4,638,111 to Gay. The RIMprocess is particularly advantageous in encapsulating photovoltaicpanels since RIM is a thermosetting polymer formed from the reaction ofinjected liquid polymeric precursors at low temperature (less than 200°F.), thus preventing heat damage to the thin film material which wouldoccur if high temperature injection molding techniques were employed. Inaddition, the use of the RIM elastomer permits the insertion of variousfastener receiving means in the elastomer during the molding process, aswill be apparent from the following description, which will acceptfasteners for the attachment of the module to various structures.

On either side of the thin film semiconductor material 22 are thin filmsof electrical conductors 24 which are patterned with a laser orotherwise, and staggered to form front and back overlapping electrodeswhich collect charge from the cell array in series. For example, a filmof zinc oxide or indium tin oxide (ITO) may be employed for atransparent front film. Aluminum and/or nickel for a non-transparent orzinc oxide or ITO for a transparent back film may be employed. Methodsfor the production and utilization of such conductor films are alsoknown in the art. If the bottom conductor layer 24 is transparent apartially reflective layer 26, for example, a coating such as a layer ofwhite or light-colored paint, may be used which causes a portion of theincident light to be reflected again through the thin film semiconductormaterial 22 after striking the reflective layer 26.

In FIG. 2, a unitary elastomer 30 is seen to encapsulate thephotovoltaic panel 12, forming a seal against a portion 32 of a frontside 34 bordering a perimeter 36 of the panel 12, and continuing aroundthe perimeter 36 and sealing against a back side 38 of the panel 12. Theencapsulation of all but the light incident portion of the front side 34of the panel 12 is a significant benefit since it eliminates thelamination step previously required in the assembly of photovoltaicmodules.

In FIG. 3 only a portion 40 of the back side 38 which is adjacent theperimeter 36 is encapsulated by the elastomer. In this FIG., the panel12 is seen to include the transparent sheet 18, thin film material 22and transparent electrical conductors 24 as described above in FIG. 2.Behind these lamina, an additional transparent sheet 19 is includedwhich protects the lamina 22 and 24 which comprise the array ofphotovoltaic cells and permits the further transmission of the incidentradiation through the panel 12 as shown to provide a totally transparentpanel.

In FIG. 3, the charge-carrying transparent conductors 24 are seen toextend from the left edge of the panel 12, where they are connected bysoldering or otherwise to means for establishing external electricalconnection to the panel 12, here shown as leads 44 and 46. These leadsare seen to include internal portions 48 and 50, which are encapsulatedby the unitary elastomer 30, and external portions 52 and 54 whichextend from the elastomer 30 for connection to an external electricalcircuit, not specifically shown, for utilization of the current producedby the photovoltaic module 10. In both FIGS. 2 and 3, the internal edgeportion of the elastomer 30 which is adjacent the front of the panel 12tapers outwardly from the panel to permit rain water or condensation todrain easily from the front of the panel when the module is placed inoperating position, that is, angled toward the sun.

In a similar manner which will be recognized by those skilled in theart, FIG. 2 shows an electrical connection means comprising connectors60 and 62 having internal portions 64 and 66 connected to thetransparent conductors 24, which establish the circuit within thephotovoltaic panel 12, by soldering or other means which are known inthe art. The internal portions 64 and 66 are seen to be embedded in theelastomer 30 so that the internal laminations of the panel 12 are sealedagainst the penetration of moisture, and the connectors 60 and 62 arethus held in congruence with the conductors 24. The connectors 60 and 62also include external portions 68 and 70 which extend from the internalportions 64 and 66 into an essentially square cavity 72 formed in theelastomer 30. This cavity 72 serves as a terminal box or junction boxfor use with a connector plug or cover plate whereby the connectors 60and 62, and the connections therewith, are isolated from theenvironment. For example a cover plate, not shown, bearing sealed wiresfor connection to an external electrical circuit may be inserted in therecess 74 provided about the edges of the cavity 72 and secured byadhesive or other fastener means. If such wires are employed, theexternal portions 68 and 70 may be threaded or otherwise adapted toreceive wire-connecting means. Alternatively, the cavity 72 may beadapted to receive an elastomeric plug which, in turn, receives theexternal portions 68 and 70 for connection with the external circuit.The general construction of terminal assemblies for prior artphotovoltaic panels is known in the art, and a particularly usefulassembly is shown in U.S. Pat. No. 4,371,739 to Lewis, et al., which isincorporated herein by reference.

Significant advantages are provided through the use of the RIM elastomermodule-forming method in that significant additional rigidity may beprovided to the photovoltaic module 10. For example, the thickness ofthe unitary elastomer overlying the back side 38 in FIG. 2, as well asthe uniform sealing of the elastomer against the abutting portions ofthe panel 12, add significant rigidity to the photovoltaic module 10.Structural ridges formed in the elastomer 30 across the back side 38 maybe employed to add significant structural stiffness without increasingthe weight of the module. Alternatively, internal structural members maybe employed to stiffen the module. For example, FIG. 3 shows an L-shapedstiffening structural member 80 at the right side of the drawing, and anI-beam shaped stiffener 82 at the left. The stiffeners 80 and 82 areshown in the drawing as being formed from carbon fibers, although a widevariety of shapes, sizes and materials may be employed for thestructural reinforcing members. For example, these members may be madeof polymeric material, steel or aluminum.

While reaction injection molding (RIM) has not previously been employedin the encapsulation of photovoltaic panels, RIM is a well establishedprocess for molding block polymers, and a wide variety of RIM machinesis in existence and known in the art. The RIM machine meters, mixes anddispenses reactive chemicals into a mold, where a chemical reactionoccurs and the desired part is formed. Polyurethanes, polyamines,epoxies, polyesters, nylon and hybrid block polymers may be formed byRIM technology and adaptable to the formation of theelastomer-encapsulated photovoltaic panels of the invention. Withrespect to the polymers formed around the photovoltaic panels, anelastomer is preferred to minimize unequal thermal expansion which mightotherwise stress the laminations of the photovoltaic panel or break theglass substrate of the panel. Preferably, an elastomer having a modulusof elasticity of from 200 to 10,000 p.s.i. is preferred. Sincepolyurethane technology is developed and easily adaptable to theencapsulation of photovoltaic panels, the use of polyurethane resins inRIM technology will be discussed in this preferred embodiment. However,other polymer systems are equally adaptable to the invention upon thereading of this description. A description of the RIM technology for awide variety of polymers is set forth in Sweeney, Reaction InjectionMolding Machinery and Processes, Marcel Dekker, Inc., New York (1987)and Kresta, Reaction Injection Molding and Fast PolymerizationReactions, Polymer Science and Technology, Volume 18, Plenum Press, NewYork (1982). Both of these publications are incorporated herein byreference.

Commercial RIM polyurethane polymer precursors are based on isocyanates,polyols, extenders, catalysts and blowing agents. The extenders areusually glycols or amines or some combination of the two. The mostcommon isocyanate is diphenylmethane diisocyanate (MDI) and has beenfound to be a preferred isocyanate in the production of the photovoltaicmodules of the invention. The polyol may be either a polyether orpolyester chain compound having reactive hydroxyl end groups.Preferably, a polyol comprising a mixture of diol-triol, or an all triolpolyol, having a molecular weight of about 4,000 is preferred. Diamineextenders such as diethyl toluene diamine have been found to beparticularly useful, as have triamine catalysts, organo-tin or tin oxidecatalysts. The elastomers of the invention may be either solidelastomers, or include a freon expanding agent to form a foam orsemifoam elastomer. Either the solid or expanded elastomer is equallyadaptable to encapsulating the photovoltaic panels of the invention. Inaddition, a wide variety of fillers may be employed to form a reinforcedreaction injection molding (RRIM) elastomer. Fillers such as carbonblack or fine limestone may be added as pigments to the elastomer.Plate-like fillers such as the mineral wollastonite may be employed asreinforcing fillers. In addition, needle-like or long fibrous fillerssuch as glass fibers may also be employed to provide structural rigidityto the elastomer.

Solid elastomers or structural RIM foam are equally adaptable to theinvention. Solid elastomers are formulated with no expanding agent andthe mold is completely filled with the polyurethane precursors.Structural foam is produced by using a chemical system containing arelatively large amount of an expanding agent such as freon. Heat fromthe chemical reaction vaporizes the expanding agent, causing thereactants to foam, adding additional expansion pressure to fill and packthe mold. The rate of the polymerization reaction is adjustedcatalytically to allow the foaming to occur before viscosity increasesexcessively.

Polyurethane precursors which are prepared specifically for use inreaction injection molding are available from BASF WyandotteCorporation, Dow Chemical Company, ICI (Rubicon), Mobay ChemicalCorporation, Olin Chemical Company, Texaco Chemicals, Union CarbideCorporation and the Upjohn Company. RIM polyurethane preparations soldunder the trade names Mobay MP 5000 and Dow Spectrim 5 have been foundto be particularly useful in the encapsulation of solar panels.

RIM machines for dispensing reactants are available from a number ofsuppliers, and are widely known and used in the art for the formation ofa wide variety of products. One source for RIM machines is AdmiralEquipment, Incorporated of Akron, Ohio. The RIM dispensing machineperforms four functions: (a) conditions the elastomer precursors tocontrol density and viscosity, (b) meters the precursors as required bythe stoichiometry of the chemical system, (c) mixes the reactants byhigh pressure impingement within the mixing head, and (d) recirculatesthe reactants to maintain pressure, density and viscosity. The meteringpumps on RIM machines may be linear, axial or rotary piston pumps, orlance pistons. The elastomer precursors are fed at high pressure to amixing head which mixes the reactants by impingement during shots,recirculates the reactants between shots, develops the pressures neededfor good mixing and self-cleans the mixing chamber using a cleanoutpiston.

As mentioned, the mixing of the reactants occurs in the mix head andcontinues after injection within the mold. The mold shapes the part,directs reactants into the mold cavity, directs the flow of reactants,controls the exotherm temperature produced by the molding process byremoving heat, and contains devices to facilitate holding the part to bemolded in position and facilitating part removal.

FIG. 4 shows a cross-sectional view of a mold 100 for forming theencapsulated photovoltaic panel of the invention. The mold 100 includesa first mold section 102 and a second mold section 104 which have facingsurfaces, detailed more specifically herein, which cooperate to define achamber for receiving the photovoltaic panel 12 and forming anencapsulated elastomer around the panel. An overhead view of the moldsection 102 is shown in FIG. 5. The mold sections 102 and 104 are seento be adaptable to be brought into a contacting relationship whereinfacing surfaces 106 and 108 abut. Mold carrying clamps for this purposeare known in the art and may comprise hydraulic or mechanical means formoving the mold sections in opposite directions as shown in FIG. 4, ormay involve a hinged book-type opening method. Such mold clamps providethe forces which hold the mold together during filling, provide thebreakaway forces necessary to open the mold after the reactants havepolymerized, move the mold from a loading position to a shot positionduring the molding cycle and open and close the mold for insertion ofmaterials and removal of the polymerized part. One source for such moldcarrying devices is Urethane Technology, Incorporated of Grand Haven,Mich.

A chamber for molding the encapsulated photovoltaic module 10 which isshown broadly in FIG. 2 is defined in FIG. 4 by a cavity 110 in the moldsection 102. The cavity 110 includes a border cavity portion whichencompasses the perimeter 36 of the panel 12 and overlies a portion ofthe front side 34 of the panel 12 bordering the perimeter 36. Seal means116 are positioned in the mold section 102 to be adjacent the peripheryof the front side of the panel 12, when the panel is in place within themold 100, to support the panel and seal the portion of the panel 2located interiorly of the seal means, that is, the area of the frontsurface 34 above and interior cavity portion 118, against the influx ofthe reactive molding fluid.

Several types of material may be used to make RIM molds. Epoxy molds areeasy to make and inexpensive compared to metals, but suffer from a lowheat transfer rate and a high coefficient of thermal expansion. Mostcommonly, metal molds such as nickel shell, spray metal, cast aluminum,cast zinc alloy (Kirksite), machined aluminum or machined steel arepreferred. Regardless of the mold material employed, it may be desirableto include a plurality of tubes or passages, shown schematically by thereference numeral 120 in FIG. 4, which are uniformly spaced throughoutthe mold sections and provide for the circulation of a heat-transferfluid in order to control the temperature at appropriate portions of themold to control chemical reaction rates. The seal means 116 and othercavity-defining portions of the mold are preferably machined orotherwise formed from metal, although resilient seal means such assilicone rubber seals may be employed.

During the molding process, the panel 12 is held against the seal means116 by a vacuum in the interior cavity portion 118 which is produced, inthe mold shown in FIG. 4, by a vacuum chuck means 122, or a plurality ofindividual vacuum cups, are employed to hold the panel 12 in a sealingrelationship with the seal means 116. The vacuum chuck 122 is seen toinclude a threaded tap 124 for attachment of a vacuum hose, not shown.When the panel 12 is thus held against the seal means 116 and the moldsections 102 and 104 are brought into an abutting relationship, a coreportion 128 of the mold section 104 is seen to be adapted to form aportion of the elastomer 30 which overlies the back side 38 of thepanel. If a transparent module such as that shown in FIG. 3 is desired,a module wherein the elastomer borders only a portion of the back side38 of the panel 12, seal means similar to the means 116 are included inthe core 128.

The mold section 102 also includes an inlet sprue 130, which is adaptedto receive the mixing and injection valve of the RIM machine, notspecifically shown. Communicating with the sprue 130 is a runner 132which preferably extends longitudinally along the length of the panel 12and which is adapted to receive the incoming fluid from the sprue 130.Upon filling, the runner 132 creates a reservoir of increased pressurewhereby the fluid elastomer precursors quickly flow over a restrictedinlet gate 134 into the nearest border cavity portion 112 and the core128 of the mold section 104. The inlet gate 134 provides a clearanceagainst the facing surface 108 of about 30/1000ths of an inch.Thereafter, the fluid fills the circumferential border cavity 112 andflows over an outlet gate 136, on three sides of the panel, and into adump well 138. It should be understood that gates 134 and 136 cooperateto extend around the periphery of the border 16 of the module 10 to formflash portions of the elastomer which are then trimmed from the module.An exit sprue 139 for excess elastomer-forming reactants may also beprovided leading from the dump well 138. It should be understood thatthe abutting perimeter portions of the mold sections 102 and 104 providesufficient clearance for the escape of air from the mold cavity.Generally, a clearance of from 5/1000ths to 10/1000ths of an inch issufficient clearance between the mold sections at 136 to allow theescape of air during the influx of the fluid.

It will be appreciated by those of skill in the art that mold design canvary significantly with respect to the dumping of excesselastomer-forming precursors, depending on factors such as the size ofthe panel to be encapsulated and the particular formulation employed.For example, while panels have been formed using the peripheral dumpwell 138 as is shown in FIG. 5, other panels have been formed in moldswherein the dump well is deleted and the border cavity 112 communicatesacross the outlet gate 136 directly with the exit sprue 139. Other moldshave been employed wherein the mold-facing surfaces 106 and 108 are insuch close contact at the gate 136 that virtually all of the elastomerflows through a single exit sprue. This provides for significantadvantages in demolding and finishing the encapsulated photovoltaicmodule. Such variations will be apparent to those with skill in the artwithout departing from the spirit of the invention.

The mold sections 102 and 104 may also be adapted, according to meansknown in the art, to form the cavity 72 or other portions of theelastomer 30 necessary to form connector means or junction boxes aroundthe external portion of the terminal assemblies which are electricallyconnected to the panel 12. For example, to form the cavity 72 in FIG. 2,an essentially square (from an overhead view) mold plug 140, shown inFIG. 4 and in some detail in FIG. 6, is inserted over the terminalmeans. The plug 140 may be made from a resilient material which iscoated with a mold-released formulation, and is seen to includecylindrical perforations 142 and 144 which cover and seal against theexposed, external portions 68 and 70 of the connectors 60 and 62. Whenthe mold sections 102 and 104 are closed, a top 146 of the mold plug 140is seen to contact the top of the core 128 so that the cavity 72 in theelastomer 30 (as shown in FIG. 2) is formed. Other means for formingconnector means or terminal boxes will be apparent to one of ordinaryskill in the art having read this disclosure. It is to be noted withrespect to the plug 140 that the edges thereof are tapered inwardly at adraft angle of at least 1.5.°, and preferably from 3° to 5° fromperpendicular. This draft angle should also be noted with respect to theedges of the elastomer 30 in FIGS. 2 and 3. Similar draft angles arealso shown with respect to the cavity 110 and the core 128 in FIG. 4.

Should it be desired to include structural means such as those shown bythe reference numerals 80 and 82 within the elastomer, these members areattached, by elastomeric adhesive or other means, to the panel 12 andthe incoming elastomer-forming fluid easily flows about the structuralmembers and any voids between the members and the panel to form a rigid,stiffened solar module.

In the method of the invention, the glass or transparent polymer withthe photovoltaic cells or films attached, as well as the structuralstiffening members and terminal members if desired, is first primed inall areas to which the elastomer is to adhere. This prime coating may ormay not be tinted to provide a partially reflective coating to thephotovoltaic panel such as that shown by the reference numeral 26 inFIG. 2. The primer is deposited about 1/4 of an inch around the edge ofthe front surface of the panel, the edges and the back. If a transparentpanel is desired, only a portion of the back surface is primed andcoated with elastomer. Primers for use in reaction injection molding areknown in the art, but the inclusion of an amino-silane coupling agent ispreferred. Epoxy-silane is also useful as is any other molecule having aportion which bonds to the elastomer and another portion which bonds tothe panel. Following the priming of the panel, the mold cavity issprayed with a mold release agent which may include a paint which colorsthe exterior of the elastomer. Such in-mold coatings are also known inthe art.

Following the priming of the panel and the in-mold coating, the primedpanel is placed in the mold, the mold closed and clamped, and a vacuumapplied to the vacuum chuck means to hold the panel securely against theseals. The clamped mold is then rotated to position the air vents at thehighest point, usually with the fluid input at the lowest point, and thefluid elastomer precursors are mixed in the mix head during theinjection process and the reacting solution is injected into the inletsprue. The impingement pressure necessary to mix the incoming streams ofpolyurethane-forming precursors in the mix head is about 2,000-3,000p.s.i., although the pressure in the mold cavity after flow through therunner and across the inlet gate is only about 20-50 p.s.i. During thepolyurethane-forming reaction, the temperature produced by thepolyurethane exotherm is maintained at about 150°-160° F. by the moldand the heat transfer fluid in the passages 120. The volume of the fluidinjected into the mold is calculated so that the elastomer-forming fluidfills the mold cavity, extends across the land or flash areas above theperipheral gates 134 and 136, and penetrates slightly into the dumpwell. Following the curing of the elastomer, which generally occurswithin thirty seconds, the encapsulated panel is removed when the moldopens. If desired, knockout pins or knockout pads may be inserted in themold section which retains the panel to facilitate part removal. Afterremoval from the mold, the encapsulating elastomeric material has a formwhich is shown schematically, in cross-section, in FIG. 7. The panel 12is there shown to be encased in a unitary elastomer 30 which extendsacross the back side 38 of the panel 12, around the perimeter 36 andoverlying and sealing against a portion of the front side 34 of thepanel bordering the perimeter. The portion of the elastomer which hascured within the inlet sprue 130 and the runner 132 is seen as beingattached to the module 10 by an inlet flash portion 150. The portion ofthe elastomer which has escaped into the dump well 138 is seen to beattached to the module 10 by a peripheral outlet flash portion 152.These flash portions are thereafter trimmed or torn from the module 10as is known in the art.

A particularly advantageous embodiment of the module 10 is shown in FIG.8. In this figure, the module 10 is seen to include a first or fronttransparent sheet 160, having front and back sides and edges forming aperimeter as shown above with respect to the sheet of substrate 18, andhaving an plurality of photovoltaic cells 162 arrayed on the back sidethereof which are capable of converting radiation incident on the frontside of the sheet 160 to electrical energy. As with all transparentsheets employed in the construction of solar panels, the sheet ispreferably plain glass having a thickness of about 2 mm rather thantempered glass since the temperature associated with the processing ofthe photovoltaic cells thereon destroys the temper of tempered glass.

The module in FIG. 8 also includes a second or back sheet 164, alsohaving front and back sides and edges forming a perimeter, the secondsheet being disposed essentially planar to and adjacent the back sidethe first sheet. The sheet 164 is preferably a tempered window glasssheet having a thickness of about 1/8 inch, the tempered glass beingemployed to provide greater strength to the module in this embodiment.

The module further includes a reaction injection molded elastomer 170which is seen in the FIG. to have an edge portion 172 which encapsulatesthe perimeter edges of the first and second sheet, and a portion of thefront side of the first sheet bordering the perimeter. At least theedges of the second sheet are encapsulated, although the elastomer canbe continued behind the back of the sheet 164 if desired to add strengthto the module.

Of particular note in this embodiment is the fact that the elastomer 170includes a portion 174 which forms a "sandwich" between the back side ofthe first sheet, that is, the side which includes the cell array 162,and the front side of the second sheet 164. Preferably, this portion 174has a thickness of from about 0.060 to about 0.10 inches, or greater,and is unitary with all edge portions 172 which form the perimeter ofthe module. This double sheet-elastomer core construction providessignificant advantages of added strength and durability. Since temperedglass cannot be used for photovoltaic panels, modules without RIMencapsulated edges can suffer breakage of the panel simply by thetorsional stress of lifting the module by one end. The single sheet RIMencapsulated panels are more durable in that the elastomer of theinvention provides an advantageous soft edge for protection of thepanel, but in tests breakage of an elastomer encapsulated single-panelhas occurred if such a panel is dropped on a carpet from a height oftwenty inches. In identical tests the double sheet-elastomer coreconstruction module shown in FIG. 8 was dropped from a height of greaterthan six feet on a concrete floor without breakage of either panel.

Further, the double sheet-elastomer core construction is balanced from athermal standpoint when sheets of comparable modulus are used in thatboth sheets expand or contract equally with temperature variations. Inaddition, the use of glass as a backing sheet is useful in that thepenetration of water vapor, which penetrates polyurethane to someextent, is minimized.

The double sheet-elastomer core module may be formed in a mold similarto the mold 100 by spacing the sheet 160 from the sheet 164 with doublesided tape of sufficient thickness, for example, a closed cellpolyurethane foam tape with acrylic adhesive on both sides. Flowrestrictors may be provided on the edges of the mold cavity, ifnecessary, so that flow of the elastomer precursors between the sheetsis accomplished without the formation of air bubbles. Alternatively,vacuum chuck means may be provided in both of the mold sections to spacethe sheets sufficiently for the influx of the RIM precursors.

The module in FIG. 8 also includes an alternative connection means 180for establishing electrical connection to the photovoltaic array 162.This connector means includes an internal portion, not specificallyshown, connected to the conductors in the cell array, and an externalportion which includes insulated wires 182 and 184 which are sealed inthe elastomer 170, and a plug 186 comprising a shaft-like connector 188and a shaft-receiving connector 190. A connector-receiving means isformed in the top edge 172 of the elastomer 170, and includes a firstcavity portion 190 positioned where the wires exit the elastomer, aplug-receiving cavity 192, and a first wire-receiving channel 194therebetween which includes wire retaining flanges 196.

In use, the plug 186 is connected to a mating plug which will conductelectricity from the module to an external device. These two plugs aresized so that the mated plug combination, when inserted in the cavity192, is securely retained by the resilient elastomer 170. The wireswhich lead from the mating plug are retained in a second wire-receivingchannel 200, including retaining flanges 202, and lead to the edge ofthe module. Depending upon the desired position of the module, the wiresand plug 186 may lead upwards from the module as shown by the phantomlines 204 for connection to the mating plug, or behind the back of themodule as displayed in that Figure.

The connector-receiving means, that is, cavities 190 and 192 and thechannels 194 and 200, may be formed by the use of a mold plug ofappropriate form, similar to the mold plug 140 shown in FIG. 6. Theexternal portion of the wires 182, 184 are positioned in grooves in theoutlet gate of the mold, for example, grooves with an elastomeric sealwhich seal tightly against the wires, and the plug 186 is positionedoutside the mold cavity during the molding process.

From the foregoing description, one skilled in the art can readilyascertain the essential characteristics of the invention and, withoutdeparting from the spirit and scope thereof, can adapt the invention tovarious usages and conditions. Changes in form and the substitution ofequivalents are contemplated as circumstances may suggest or renderexpedient, and although specific terms have been employed herein, theyare intended in a descriptive sense and not for purposes of limitation,the purview of the invention being delineated in the following claims.

What is claimed is:
 1. A photovoltaic module comprising:a panel havingfront and back sides and edges forming a perimeter and at least onephotovoltaic cell capable of converting radiation incident the frontside of the panel to electrical energy; and a unitary, reactioninjection molded elastomer partially encapsulating the panel and forminga seal against a portion of the front side of the panel bordering theperimeter, continuing around the perimeter and encapsulating the entireback side of the panel.
 2. The photovoltaic module of claim 1 whereinthe panel further includes means for establishing external electricalconnection to the at least one photovoltaic cell including an internalportion electrically connected to the cell and an external portionextending from the panel, and the unitary elastomer further encapsulatesthe internal portion of the connecting means.
 3. A photovoltaic modulecomprising:a panel having (a) front and back sides and edges forming aperimeter, (b) at least one photovoltaic cell capable of convertingradiation incident the front side of the panel to electrical energy, and(c) means for establishing external electrical connection to the atleast one photovoltaic cell, including an internal portion electricallyconnected to the at least one cell and an external portion extendingfrom the panel; and a unitary, reaction injection molded elastomerencapsulating the entire back side and perimeter edges of the panel andforming a seal against a portion of the front side of the panelbordering the perimeter, the unitary elastomer further encapsulating theinternal portion of the terminal means.
 4. A photovoltaic modulecomprising:a first sheet having front and back sides, and edges forminga perimeter, and at least one photovoltaic cell capable of convertingradiation incident the front side of the sheet to electrical energy; asecond sheet disposed parallel to the first sheet and adjacent the backside thereof; a unitary, reaction injection molded elastomer disposedbetween the back side of the first sheet and the second sheet, theelastomer partially encapsulating the first sheet, forming a sealagainst a portion of the front side of the first sheet bordering theperimeter, continuing around the perimeter of the first sheet andsealing against at least a portion of the second sheet.
 5. The module ofclaim 4 wherein the second sheet has front and back sides and edgesforming a perimeter, and the front side of the second sheet is securedto the back side of the first sheet by the reaction injection moldedelastomer, the elastomer further encapsulating the edges of the secondsheet.
 6. A photovoltaic module comprising:a first sheet having (a)front and back sides and edges forming a perimeter, (b) at least onephotovoltaic cell capable of converting radiation incident the frontside of the sheet to electrical energy, and (c) means for establishingexternal electrical connection to the photovoltaic cell, including aninternal portion electrically connected to the cell and an externalportion extending from the sheet; a second sheet, having front and backsides and edges forming a perimeter, the second sheet being disposedparallel the first sheet and adjacent the back side thereof; and aunitary, reaction injection molded elastomer (a) encapsulating theperimeter edges and a portion of the front side of the first sheetbordering the perimeter, (b) disposed between the back side of the firstsheet and the front side of the second sheet, (c) encapsulating theedges of the second sheet, and (d) further encapsulating the conductiveportion of the terminal means.
 7. A photovoltaic module comprising:afirst sheet having front and back sides and edges forming a perimeterand at least one photovoltaic cell capable of converting radiationincident the front side of the sheet to electrical energy; a secondsheet, having front and back sides and edges forming a perimeter,disposed parallel to the first sheet and adjacent the back side thereof;and the first and second sheets being joined by a unitary, reactioninjection molded elastomer disposed between the back side of the firstsheet and the front side of the second sheet, encapsulating theperimeter edges and a portion of the front side of the first sheetbordering the perimeter, and continuing around the perimeter edges ofthe first sheet and encapsulating the edges of the second sheet.
 8. Themodule of claim 8 which further includes means for establishing externalelectrical connection to the photovoltaic cell, including an internalportion electrically connected to the cell and an external portionextending from the first sheet, and wherein the internal portion of theterminal means is further encapsulated in the unitary, reactioninjection molded elastomer.